Radome and method of making same

ABSTRACT

A radome is described which is formed from resin-impregnated glass, quartz, or other fiber sheets which are folded to provide longitudinally extending radial ribs. The folds are formed by means of a tool made up of several sector-shaped members. These members are matched along one edge and the sheet, while pliable, is formed into double thickness folds between adjacent ones of the members. The sector shaped members are clamped together as each fold is made to provide the ribs.

United States Patent 11 Claims, 13 Drawing Figs.

u.s.c| 343/872,

264/257 Int.Cl noun/42 FieldofSearch 156/204,

[56] References Cited UNITED STATES PATENTS 3,349,157 10/1967 Parsons 264/258 3,444,558 5/1969 Leitner 343/872 OTHER REFERENCES Oleesky & Mohr, Handbook of Reinforced Plastics, Feb, 21, [964, pp. [33- l3t5, copy 343 872 Primary Examiner-Eli Lieberman Atmmey- Martin Lukacher ABSTRACT: A radome is described which is formed from resin-impregnated glass, quartz, or other fiber sheets which are folded to provide longitudinally extending radial ribs. The folds are formed by means ofa tool made up of several sectorshaped members. These members are matched along one edge and the sheet, while pliable, is formed into double thickness folds between adjacent ones of the members. The sector shaped members are clamped together as each fold is made to provide the ribs.

PATENTEUNBVZ l n 3.618.112

SHEET 2 [1F 4 INV/z'N'lT/k. 5 RUBERTJ. GRUVE AND MERRILL M FEEDER ATTORNEY PATENTED NUVZ SHEET 3 [1F 4 u mq R a zr/J 11v v1 1v 1 (m ROBERT J GROVE 4N0 MERRILL M. REEDER ATTORNEY PATENTED 1111112 1911 SHEET 0F 4 OVE AND N'I'OR. RT J. 67? MERRILL M. REEDER [N V11 ROBE A TTORNE Y RADOME AND METHOD OF MAKING SAME The present invention relates to radomes and methods of making same and particularly to a radome having longitudinal ribs which are formed with the aid of a clamping tool.

The invention is especially suitable for use in fabricating a radome of the type described in U.S. Pat. application, Ser. No.

752,948, filed Aug. 15, 1968, in the names of Gus P. Tricoles andEugene L. Rope andassigned to the same assignee as this application now U.S.Pat. No. 3,576,581. As described in the Tricoles and Rope application, longitudinally extending ribs improve the radiation transmission characteristics of the radome.

Radomes, in order to minimally interfere with the transmission of microwave energy are desirably very thin walled. The radomes must, however, be structurally strong in order to withstand the forces applied thereto when they are operationally in the nose of an aircraft. Inasmuch as these two desirable properties are contradictory, much effort has been directed towards providing a thick radome which has the necessary structural properties and yet does not interfere with the transmission of radiation. It has been found, as described in the abovereferenced Tricoles and Rope application, that radomes transmissivity may be enhanced and, in fact, improved by equipping the radome with ribs.

Accordingly, it is an object of this invention to provide an improved radome in which ribs are fabricated in a manner to provide structural rigidity and strength while providing thin wall construction.

It is a further object of the invention to provide a radome in which the walls of the structure as well as the ribs are thin.

It is a still further object of the invention to provide an improved radome having stiffeners, which apply structural rigidity thereto, formed as an integral part of the structure.

It is a still further object of the invention to provide an improved method manufacturing a radome.

It is a still further object of the invention to provide an improved method of fabricating structural rigid parts of thin sheet material, which parts are especially suitable for use in radomes.

It is a still further object of the invention to provide an improved method ofmanufacturing internally ribbed shells.

It is a still further object of the invention to provide an improved method of manufacturing laminated radomes.

Briefly described, a radome embodying the invention is formed as a sheet of pliant material such as cloth which may be impregnated with epoxy, polyester, polyimide or similar resins. A tool is used which has a plurality of sector-shaped members; the outer surfaces ofwhich define the shape of the radome. The sheet is placed over each of the sector-shaped portions in sequence and folds are formed between adjacent sector-shaped members. The members are then clamped together and the entire structure stiffened, as by curing a resin impregnated in the cloth. If desired, the ribbed radome structure may be laminated to an outer shell of similar material to provide an especially strong and rigid structure.

The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof will become more readily apparent from a reading of the following description in connection with the accompanying drawings in which:

FIG. I is a perspective view of a radome in accordance with the present invention, the view being broken away and partially shown in phantom in order to illustrate the internal construction of the radome;

FIG. 2 is a top view of one of the ribbed segments which is used in constructing the radome shown in FIG. 1;

FIG. 3 is a side view of the ribbed segment shown in FIG. 2;

FIG. 4 is an exploded view of the tool used to make the ribbed segment shown in FIGS. 2 and 3;

FIGS. 5a through 5e are end views illustrating the steps involved in the method of making the ribbed segment shown in FIGS. 2 and 3;

FIG. 6 is a view from the rear of the ribbed segment after the completion of the steps shown in FIGS. 5a through 5e;

FIG. 7 is a sectional view showing one of the steps in construction of the outer shell of the radome shown in FIG. 1;

FIG. 8 is a fragmentary sectional view of the apparatus shown in FIG. 7, the view taken along the line 8-8 in FIG. 7 and viewed in the direction of the arrows;

FIG. 9 isa fragmentary sectional view of the portion of the apparatus shown in FIG. 8, the section being taken along the line 9-9 when viewed in the direction of the arrows.

Referring more particularly to FIG. 1, there is shown a radome made out of an outer shell 10 and a ribbed shell 12. These shells may be made up of sheets of cloth which are very thin. The sheets are desirably impregnated with resin, such as epoxy, polyester, polyimide, or other suitable resin. The shells are laminated together to provide an essentially strong, struc turally rigid radome suitable for mounting in the nose of a missile, rocket or aircraft. The shape of both the'inner and outer shells is generally cylindrical, conical or ogive. The inner shell has a multiplicity of longitudinal ribs 14 which are desirably thin andare made up of two thicknesses of the sheet which forms the inner shell 12.

Reference may be had to the above-mentioned Tricoles and Rope application for a discussion as to how the ribs 14 improve the electrical properties of the radome and increases its transmission to radiation.

The inner shell 12 is made up of a number of segmental portions, one of which 16 is shown in FIGS. 2 and 3. The three inner ribs 14a, 14b and 14c are made up of a double thickness of the material from which the segmental portion 16 is constructed. The outer ribs 14d and 142 are made up of single thicknesses of the sheet material. Thus, when adjacent segmental portions are joined together to form the entire inner shell 12, all ribs will be made up of a double thickness of sheet material. It will therefore be observed that the ribs, as well as the shells themselves, will be exceedingly thin, say 0.020 inches. This thickness may be much, much less than a quarterwavelength of the radiation which is to be transmitted to the radome, and thus, the radome will be essentially invisible to the radiation. The ribs act as stiffeners and impart the necessary structural rigidity to the radome without requiring added thickness and weight in the shell walls.

The segmental portion 16 may be fabricated with the aid of the tool shown in FIG. 4. This tool includes a baseplate I8 and a plurality of wedgelike, sector-shaped members 20a, 20b, 20c and 20d. When the sector-shaped members 20 are disposed on the baseplate, their outer surfaces 22a, 22b, 22c and 22d are contiguous to each other and define the shape of the sector of the radome to be provided by the portion 16. The bottom surface of the members 20 have different angles with respect to the sides, so that when secured to the baseplate bymeans of screws 30 which extend through the holes in the baseplate, form the desired surface shape by their contiguous upper surfaces 22a through 22d. One side of each of the members 20a through 20d has a notch 24a, 24b, 24c and 24d. This notch extends radially downward towards the baseplate, a predetermined distance equal to the desired height of the ribs. The bottom of each notch defines a shoulder 26a, 26b, 26c and 26d. Holes 28a in the sector-shaped member 20 a and correspond ing holes 28b, 28c and 28d in members 20b, 20c and 20d are aligned with each other when the members 20a, 20b, 20c and 20d are mounted on the baseplate 18. The members may be bolted together in side-by-side relationship via these holes 28.

Referring to FIGS. 5a through 52, it will be observed that the segmelttal portion 16 is constructed by first fastening the member 20a to the baseplate 18 by means of the screws 30. The sheet of pliant material 32 is then placed on the surface 220 of the member 20a. This sheet is folded over the edges of the surface 220. In order to form the rib 140, the sheet is folded into the notch 24a until it reaches the shoulder 260. A

180 fold is then made at the shoulder 26a. Next, as shown in FIG. 5b, the next member 20b is placed against the member 20a so as to confine the fold which provides the rib 14a. An approximately fold is then made at the left edge of the member 20b, so that the sheet 32 conforms to the upper surface 22b of the member 20b. The next rib 14b is formed in the same manner as explained in connection with FIGS. 50 and 5b by making the folds in the notch 24b and placing the next number 20c against the member 20b. Each member is fastened in place by means of screws 30 on the baseplate 18. The notch 24c is then used and the process continued in order to provide the rib 14c. After all of the members 20a through 20d are assembled on the baseplate, they are clamped together by means of bolts 34. The entire structure is then placed in a vacuum chamber, auto clave or pressure boot 21 which causes the outer folds 14d and Me to conform to the notch 24d in the member 20d and against the left side wall of the member 200. The sheet 32 may then be partially or completely cured by heating in the chamber and allowing the clamped-together structure to remain in the chamber for a period of time, varying with the resin. The structure is then disassembled by removing the bolts 34 and screws 30 and the single-thickness ribs He and 14d cut to the required length. The completed segmental portion 16 is shown in FIG. 6.

In the event that an outer shell is not to be used, the several segmental portions 16 may be placed directly in a mold, such as the conically shaped mold 36, as shown in FIG. 7. A conical form (not shown) may then be placed in the mold. Additional resin may be applied to the outer surfaces of the single-thickness ribs 14c and 14d. The conical form then holds the entire structure in position by applying pressure against the ribs. The mold is then heated, if necessary, so that the resin will cure and the various segmental portions 16 will become attached to each other at the single-thickness ribs 142 and 14d.

In the event that an outer shell 10 is used, it may be desirable to build up the outer shell 10 in the mold 36 from a plurality of sheets, say layers as shown in FIG. 7 of resin-impregnated cloth. These sheets may be placed against the internal surface of the mold 36. In order to smooth out the shell and remove any excess resin or bubbles formed during curing that weaken the radome structurally, the squeegee device 40 shown in FIG. 7 may be used. This device is made up ofa helical band 42 of flexible material, such as steel which is coated on its upper surface by plastic material, the coating 44 imparting additional thickness to the helical band 42. A suitable plastic material is polytetraflourethylene, which is sold by the E. l. Dupont DeNemours Co. of Wilmington, Del., under their trademark "Teflon." The coated band 42 is mounted on a rotatable conical member 46 by means of leaf-type springs 48. Coil springs may also be used with a slight modification of the attachment. These springs may be screwed into the conical member 46 by means of attaching screws 50. The edge of the springs which are attached to the band 42 have aligned holes 52 therein. These holes may be in the form of slots through which rivets 54 which hold the springs 48 in position against the band 42, are disposed. The springs 48 may then have freedom of motion to compress and expand so as to apply the necessary spring pressure against the band and force the Teflon coating 44 against the sheets ofmaterial which define the shell 10. The conical member 46 may be rotated in order to squeegee any excess resin out of the sheets which define the shell 10 and to cause these sheets to conform to the shape of the mold. An opening (not shown) may be provided in the nose of the shell 36 through which the excess material may be forced. This nose opening may be connected to a vacuum source for draining off the excess resin. After the shell 10 is formed, the segmental portions 16 may be placed within the shell and laminated thereto, as heretofore described.

From the foregoing description, it will be apparent that there has been provided an improved radome and the method of making same. While materials which are desired in a preferred form of the invention have been described, as well as preferred forms of tools used in practicing the invention, it will be appreciated that variations and modifications therein within the scope of the invention will suggest themselves to those skilled in the art. Accordingly, the foregoing description should be taken merely as illustrative and not in any limiting sense.

We claim:

1. A radome which comprises a continuous sheet of cloth providing a shell having a generally conical slope, a plurality of radially inwardly extending ribs, each provided by a fold in said sheet which extends radially inward from the surface of said shell and is folded back upon itself and then extends radially outwardly to said surface, said ribs reinforcing said shell for improving the structural rigidity thereof and the electromagnetic wave transmissively of said radome, and said cloth being impregnated with hardened resin so as to be selfsustaining.

2. The invention as set forth in claim 1 wherein said shell is made up of a plurality of said continuous sheets each adjoining another to provide a different segment of said shell, the adjoining walls of said segments each being provided by a single thickness of said cloth extending radially inwardly of said sheet to the same extent as said fold, the single thickness ad joining walls as joined together providing additional ribs of said shell.

3. The invention as set forth in claim 2 further comprising a generally conical-shaped outer shell of hardened resin impregnated cloth, the internal surface of said outer shell being of essentially the same shape and dimensions as the external surface of said internally ribbed shell, said internally ribbed shell being disposed within said outer shell with its external surface juxtaposed secured to the internal surface of said outer shell.

4. The invention as set forth in claim 3 wherein said ribbed and outer shells are laminated to each other at their juxtaposed surfaces.

5. The method of making a radome which comprises the step of:

a. laying a sheet of pliant material over the surface of several sector-shaped members having longitudinally extending spaces therebetween,

b. folding said sheet into said spaces so that overlapping portions of said sheet form several longitudinal ribs in said sheet,

c. securing said members together to apply clamping pres sure laterally against said ribs, and

d. stiffening said sheet while it is clamped to provide a rigid body having the shape of at least a portion of said radome.

6. The invention as set forth in claim 5 wherein said sheet is impregnated with resin prior to stiffening.

7. The invention as set forth in claim 6 wherein said sheet is of fiber glass material.

8. The invention as set forth in claim 5 wherein said sectorshaped members have sides which radially extend from the curved surface over which said sheet is laid, one of said sides having a notch in the edge thereof which is formed with said curved surface, which notch forms a shoulder at a predetermined distance from said curved surface, and wherein said folding step is accomplished by laying said sheet downwardly into said notch, bending said sheet upwardly to form the fold with the bottom of said fold extending longitudinally along said shoulder, thereby having two thicknesses of said sheet in said notch, placing the unnotched side of another of said sector-shaped members in juxtaposition with said notched member in which said fold is formed so that the curved surfaces of said sector-shaped members are contiguous and continuous, bending said sheet laterally over said curved surface of said other sector-shaped member, then repeating the foregoing steps with said other sector-shaped members and said several additional sector-shaped members until said several ribs are formed.

9. The invention as set forth in claim 8 wherein said sheet is formed into a segmental portion of said radome, and including the steps of securing a plurality of said segmental portions together along their radially extending folded sides thereof to form a complete surface of revolution.

10. The invention as set forth in claim 9 further comprising the steps of laying a sheet of resin-impregnated material into a mold having the shape of said radome, placing said completed said mold of inserting a helically band of yieldable material into said mold, applying spring pressure to urge said band against said sheet, and rotating said band to squeegee any excess resin from said sheet and conform it to the shape of said 1 l. The invention as set forth ,in claim 10 including the step 5 moldperformed prior to said step of placing said ribbed portion into i i l i 

1. A radome which comprises a continuous sheet of cloth providing a shell having a generally conical slope, a plurality of radially inwardly extending ribs, each provided by a fold in said sheet which extends radially inward from the surface of said shell and is folded back 180* upon itself and then extends radially outwardly to said surface, said ribs reinforcing said shell for improving the structural rigidity thereof and the electromagnetic wave transmissively of said radome, and said cloth being impregnated with hardened resin so as to be selfsustaining.
 2. The invention as set forth in claim 1 wherein said shell is made up of a plurality of said continuous sheets each adjoining another to provide a different segment of said shell, the adjoining walls of said segments each being provided by a single thickness of said cloth extending radially inwardly of said sheet to the same extent as said fold, the single thickness adjoining walls as joined together providing additional ribs of said shell.
 3. The invention as set forth in claim 2 further comprising a generally conical-shaped outer shell of hardened resin impregnated cloth, the internal surface of said outer shell being of essentially the same shape and dimensions as the external surface of said internally ribbed shell, said internally ribbed shell being disposed within said outer shell with its external surface juxtaposed secured to the internal surface of said outer shell.
 4. The invention as set Forth in claim 3 wherein said ribbed and outer shells are laminated to each other at their juxtaposed surfaces.
 5. The method of making a radome which comprises the step of: a. laying a sheet of pliant material over the surface of several sector-shaped members having longitudinally extending spaces therebetween, b. folding said sheet into said spaces so that overlapping portions of said sheet form several longitudinal ribs in said sheet, c. securing said members together to apply clamping pressure laterally against said ribs, and d. stiffening said sheet while it is clamped to provide a rigid body having the shape of at least a portion of said radome.
 6. The invention as set forth in claim 5 wherein said sheet is impregnated with resin prior to stiffening.
 7. The invention as set forth in claim 6 wherein said sheet is of fiber glass material.
 8. The invention as set forth in claim 5 wherein said sector-shaped members have sides which radially extend from the curved surface over which said sheet is laid, one of said sides having a notch in the edge thereof which is formed with said curved surface, which notch forms a shoulder at a predetermined distance from said curved surface, and wherein said folding step is accomplished by laying said sheet downwardly into said notch, bending said sheet upwardly to form the fold with the bottom of said fold extending longitudinally along said shoulder, thereby having two thicknesses of said sheet in said notch, placing the unnotched side of another of said sector-shaped members in juxtaposition with said notched member in which said fold is formed so that the curved surfaces of said sector-shaped members are contiguous and continuous, bending said sheet laterally over said curved surface of said other sector-shaped member, then repeating the foregoing steps with said other sector-shaped members and said several additional sector-shaped members until said several ribs are formed.
 9. The invention as set forth in claim 8 wherein said sheet is formed into a segmental portion of said radome, and including the steps of securing a plurality of said segmental portions together along their radially extending folded sides thereof to form a complete surface of revolution.
 10. The invention as set forth in claim 9 further comprising the steps of laying a sheet of resin-impregnated material into a mold having the shape of said radome, placing said completed surface of revolution provided by said ribbed segmental portions within said mold so that its outer surface is in juxtaposition with said resin-impregnated sheet, and laminating said resin-impregnated sheet and said ribbed portion together.
 11. The invention as set forth in claim 10 including the step performed prior to said step of placing said ribbed portion into said mold of inserting a helically band of yieldable material into said mold, applying spring pressure to urge said band against said sheet, and rotating said band to squeegee any excess resin from said sheet and conform it to the shape of said mold. 